THIS INVENTION relates to a method of generating displacement, to a displacement generator, and to a thermo-acoustic refrigerator.
U.S. Pat. No. 5,481,152 in the name of Buschulte discloses a piezoelectric actuator including a hollow body 1 formed as a round tube 2 of piezoelectric material. At least one end of the tube mounts an elastic membrane 10 via an annular carrier member 8. The hollow body forms an enclosed chamber 13 filled with incompressible fluid 14. Operating the piezoelectric element changes the volume of the chamber and causes commensurate deformation of the elastic membrane. In another embodiment, elastic membranes are provided at both ends. In yet another embodiment, two piezoelectric tubes, one received with clearance within the other, form an annular chamber to provide more versatility in the amount of deformation of the elastic membrane which can be achieved.
In accordance with a first aspect of this invention, there is provided a displacement generator which includes
a housing defining an enclosed chamber, the housing including a port exposed to the chamber;
at least one flexible wall exposed to the chamber;
a fluid contained within the chamber;
a movable member in the port which movable member is exposed to the fluid;
a motion transducer able to generate motion and being operatively connected to said at least one flexible wall selectively to flex said at least one flexible wall.
In use, when the wall is flexed, the volume of the chamber is changed which causes movement of the fluid through the port which causes commensurate movement of the movable member which acts as a displacement output of the displacement generator.
In one species of embodiment, said at least one flexible wall may be an outer wall of the housing, forming part of an outer boundary of the chamber. Preferably, said at least one flexible wall may be a first flexible wall, the outer wall of the housing providing also an opposing second flexible wall opposite to said first flexible wall, said first and second flexible walls providing an opposing wall pair arranged to flex in opposing directions to increase/decrease a spacing therebetween, said opposing wall pair forming an enclosed actuating chamber which is said enclosed chamber. Further, said fluid may be a relatively incompressible actuating fluid, preferably a liquid, the displacement generator including a modulating chamber surrounding said actuating chamber and a relatively compressible modulating fluid, preferably a gas, at a predetermined pressure, within the modulating chamber, the flexible well pair having outer surfaces opposite to inner surfaces which are exposed to the actuating fluid, the outer surfaces being exposed to the modulating fluid. Appropriate selection of the actuating fluid and the modulating fluid in conjunction with the physical configuration of the device will then allow a desired natural frequency of the device to be obtained.
In another species of embodiment, said at least one flexible wall may be an inner wall within the housing, said housing being an outer housing defining the enclosed chamber, said at least one flexible wall forming an internal wall within the enclosed chamber. Preferably, said at least one flexible wall may be a first flexible wall, the displacement generator including also an opposing second flexible wall opposite to said first flexible wall, said first and second flexible walls providing an opposing wall pair arranged to flex in opposing directions to increase/decrease a spacing therebetween, said opposing wall pair forming an enclosed modulating chamber which is an inner chamber within said enclosed chamber, which is an actuating chamber. Further, said fluid in said actuating chamber may be relatively incompressible, e.g. a liquid, the displacement generator including a modulating fluid e.g. a gas, at a predetermined pressure, which is relatively compressible in said modulating chamber.
Said first and second flexible walls of said flexible wall pair may advantageously be curved, said motion transducer being arranged to displace opposed ends of the flexible wall pair relative to each other to change the curvature of the respective walls thus to cause a relatively large change in volume of the actuating chamber in response to a relatively small displacement of said opposing ends. Thus the motion transducer may be connected in between said opposed ends, the motion transducer being selectively extensible/contractible.
The motion transducer may be selected from the group consisting of an electrostriction device, a magnetostriction device, and a piezoelectric device, Preferably the motion transducer may be in the form of a piezoelectrical ceramic stack extending between the opposed ends.
In accordance with a second aspect of this invention, there is provided a method of generating displacement by a displacement generator which includes
a housing defining an enclosed chamber, the housing including a port exposed to the chamber;
at least one flexible wall exposed to the chamber;
a fluid contained within the chamber;
a movable member in the port which movable member is exposed to the fluid,
the method including actuating a motion transducer which is operatively connected to said at least one flexible wall selectively to flex said at least one flexible wall to change the volume of the chamber to move the movable member.
When said at least one flexible wall is an outer wall of the housing and forms part of an outer boundary of the chamber, and when said at least one flexible wall is a first flexible well, the outer wall of the housing providing also an opposing second flexible wall opposite to said first flexible wall, said first and second flexible walls providing an opposing wall pair forming an enclosed actuating chamber which is said enclosed chamber, the method may include selectively flexing, by means of said motion transducer, said opposing wall pair in opposing directions to increase/decrease a spacing between the first and second flexible walls.
When said fluid is a relatively incompressible actuating fluid, and the displacement generator includes a modulating chamber surrounding said actuating chamber and a relatively compressible modulating fluid within the modulating chamber, the flexible wall pair having inner surfaces which are exposed to the actuating fluid and outer surfaces opposite to the inner surfaces, the outer surfaces being exposed to the modulating fluid, the method may include modulating the change in volume of the actuating chamber by resiliently resisting said change in volume by means of the modulating fluid.
When said at least one flexible wall is an inner wall within the housing, said housing being an outer housing wall defining the enclosed chamber, and when said at least one flexible wall is a first flexible wall, the displacement generator including also an opposing second flexible wall opposite to said first flexible wall, said first and second flexible walls providing an opposing wall pair internally within the enclosed chamber, the opposing well pair being arranged to flax in opposing directions to increase/decrease a spacing therebetween, said opposing wall pair forming an enclosed modulating chamber which is an inner chamber within said enclosed chamber, the enclosed chamber being an actuating chamber, said fluid in said actuating chamber being relatively incompressible, the displacement generator including a modulating fluid which is relatively compressible in said modulating chamber, the method may include modulating the change in volume of the actuating chamber by resiliently resisting said change in volume by means of the modulating fluid.
When said first and second flexible walls of said flexible wall pair are curved, the method may include displacing, by means of said motion transducer, opposed ends of the flexible wall pair relative to each other to change the curvature of the respective walls thus to cause a relatively large change in volume of the actuating chamber in response to a relatively small displacement of said opposing ends.
The motion transducer may be connected in between said opposed ends, actuation of the motion transducer being selectively extending or contracting the motion transducer.
In accordance with a third aspect of this invention, there is provided a thermo-acoustic refrigerator including a resonator and a displacement generator drivingly connected to the resonator, the displacement generator being in accordance with the first aspect of this invention.